1. Field of the Invention
This invention relates to a novel process of manufacturing ketenes.
2. Description of Related Art
Ketenes are highly reactive chemical intermediates of the general form RR'C.dbd.C.dbd.O. Ketenes find application as powerful acylating agents for a range of compounds. Alkyl ketene dimers (AKD) are produced from long chain (C.sub.8 -C.sub.32)fatty acids for use as paper sizing agents.
While there exist a variety of routes to ketenes, these do not generally involve heterogeneous catalysis. Low molecular weight ketenes are produced by thermal pyrolysis of carboxylic acids or ketones at 600.degree.-800.degree. C. (Encyclopedia of Polymer Science and Technology, Vol. 8, Interscience, New York, (1968), p. 45, Rice, F. O., Greenberg, J., Waters, C. E., Vollrath, R. E., J. Am. Chem. Soc. 56, 1760 (1934), Hurd, C. D. and Roe, A., J. Am. Chem. Soc. 61, 3355 (1939), Hurd, C. D. and Martin, K. E., J. Am. Chem. Soc. 51, 3614 (1929), Bamford, C. H. and Dewar, J. S., J. Chem. Soc., 2877 (1949) and Guenther, W. B. and Walters, W. D., J. Am. Chem. Soc. 81, 1310 (1959)). Higher molecular weight ketenes are produced by dehalogenation of .alpha.-halo acyl halides or dehydrohalogenation of acyl halides with tertiary amines as disclosed in U.S. Pat. No. 2,383,863 issued to R. Heuter and U.S. Pat. No. 3,535,383 issued to E. S. Rothman. None of these routes enjoys the efficiency of a catalytic process. The dehalogenation-based processes are multistep organic syntheses which utilize hazardous reagents, e.g. phosgene, and solvents, and yield undesirable by-products. Thus efficiency, safety and waste minimization imperatives all favor the development of a one-step catalytic process.
Gun'ko and coworkers (Brei, V. V., Gun'ko, V. M., Khavryuchenko, V. D., Chuiko, A. A.,, Kinetics and Catalysis 31, 1019 (1991), Brei, V. V., Gun'ko, V. M. Dudnik, V. V., Chuiko, A. A., Langmuir, 8, (1992), and Gun'ko, V. M., Brei, V. V., Chuiko, A. A., Kinetics and Catalysis 32, 91 (1991)) observed the formation of ketene in temperature programmed desorption "TPD" experiments in which acetic acid and acetyl chloride were employed to synthesize acetoxysilyl groups on aerosils.
U.S. Pat. No. 3,366,689 issued to Maeda et al. describes a process for manufacturing ketenes by contact dehydration for aliphatic carboxylic acids having 3 to 6 carbon atoms with a silica catalyst having a specific surface area of less than 100 m.sup.2 /g. and at a temperature of 400.degree.-900.degree. C. The silica catalyst may be diatomaceous earth, pumice, acid clay, kaolin, aluminum silicate, magnesium silicate or silica-boric oxide.
U.S. Pat. No. 2,175,811 issued to Loder describes a process for preparation of ketene which comprises thermally decomposing lower aliphatic monocarboxylic acid esters in the vapor phase at 500.degree.-1000.degree. C. in contact with a catalyst which can be silica gel supporting a promoter such as phosphoric acid or boron oxide.
U.S. Pat. No. 2,295,644 issued to Fallows et al. describes a process for manufacturing ketene and acetic anhydride by thermal dehydration of acetic acid vapors in the presence of a catalyst by passing the vapors at 500.degree.-1000.degree. C. over pumice with zinc oxide or cadmium oxide deposited on the surface.
U.S. Pat. No. 1,870,104 issued to Dreyfus describes a process for the manufacture of ketene, acetic acid or acetic anhydride or mixture thereof which comprises passing vapors of acetic acid and acetaldehyde at 500.degree.-600.degree. C. over a catalyst selected from a group which includes pumice.
U.S. Pat. No. 2,108,829 issued to Sixt et al. describes a catalytic process for producing ketene which comprises subjecting acetic acid vapors containing acetic anhydride forming catalyst to heating at a temperature between 500.degree.-1000.degree. C. under partial vacuum and immediately separating ketene from the other components. Solid catalysts, such as pea size "carborundum" coated with sodium metaphosphate, may be used (Example 1).